The vulnerability description explicitly mentions that the downloadAction is affected by an Insecure Direct Object Reference via the downloaduid parameter. The provided commit 99b07497f5842a59e934583283e1b5a477ce79a9 modifies the Classes/Controller/ManagerController.php file, specifically the downloadAction method. The changes involve adding logic to load allowed file collections and then verifying that the downloaduid (referred to as $recordUid in the code) is present within these collections. The absence of this check in the vulnerable versions allowed attackers to access arbitrary files. Therefore, the downloadAction function is the vulnerable function as it directly processed the user-controlled downloaduid parameter without sufficient authorization checks.